//leetcode:21.合并两个有序链表


/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        ListNode newHead = new ListNode(-1);
        ListNode tmp = newHead;
        while(list1!=null && list2!=null) {
            if(list1.val<=list2.val) {
                tmp.next = list1;
                list1 = list1.next;
                tmp = tmp.next;
            } else {
                tmp.next = list2;
                list2 = list2.next;
                tmp = tmp.next;
            }
        }
        if(list1 == null) {
            while(list2 != null) {
                tmp.next = list2;
                list2 = list2.next;
                tmp = tmp.next;
            }
        }
        if(list2 == null) {
            while(list1 != null) {
                tmp.next = list1;
                list1 = list1.next;
                tmp = tmp.next;
            }
        }
        return newHead.next;
    }
}